How would you like to have free hot water for the next 40 years? That should sound pretty good — about 15 percent to 20 percent of a typical household’s energy outlay goes to make sure the “H” tap means what it says. If energy prices increase by 6 percent annually, the average family would save thousands of dollars over the coming decades by installing a solar water-heating system that supplies just 65 percent of their hot water.

Sol-Reliant hot water system from Mr. Sun Solar in Beaverton

I mean “free” literally. Yes, you’ll spend money up front to install the heating system, but your home equity will increase instantly, often enough to offset the cost of installation. You’ll also pay reduced utility bills — saving more money every time rates rise. Within a few years, you’ll recover the initial expense. Experts agree, a solar water heater is far and away the easiest initial investment in renewable energy. Perhaps best of all, you’ll enjoy hot baths or showers with the satisfaction of knowing the energy comes directly from the sun.

A Good Deal, Getting Better

Solar water heaters vary in their details, but they all do the same basic things: gather heat in a solar collector; transfer the heat, directly or indirectly, to the water supply; and store the heated water until it’s used. They use relatively simple, time-tested technology, which is one reason they are a best bet in renewable energy.

It’s important to understand that solar water-heating systems have very low — sometimes zero — operating costs, and maintenance amounts to only about $2 per month. Say you might spend $7,000 to install a solar water heater, when you could install a conventional gas or electric heater for considerably less. But it’s so much less expensive to operate the solar heater that, at some point, you’ll make up the initial difference. When all costs for purchase, installation, maintenance and operation are taken into account, a solar water heater usually equals an electric heater after just eight and a half years, and equals a gas heater in just less than 15 years. From then on, through the expected 40-year life of the solar system, you’ve got free hot water (see “Gas vs. Solar: Compare Costs,” in the Image Gallery).

Consider the positive environmental benefits of a solar water heater, and the deal just gets better. A typical residential solar water heater will offset greenhouse gas emissions by about 1,500 pounds of carbon dioxide (CO2) per year. That’s equal to the amount of CO2 released by an average vehicle every 1,685 miles (based on 19.6 pounds of CO2 per gallon at 22 mpg).

It’s cheaper to conserve energy than to purchase it, so the first thing you’ll want to do is reduce your hot water needs to the minimum. Start by reducing waste; then minimize consumption. Reducing your usage ensures that your solar heating system will provide the maximum possible portion of your hot water. Even if you don’t go solar, using the minimum necessary hot water is good for your wallet and good for the environment.

The next step is to choose a solar water heater to supplement your fossil-fueled heater. Here are the first things you need to consider about a solar water heater:

Siting. Solar collectors must be in full or nearly full sunlight all year, so have a solar professional assess your site to find the best location for the collector. The optimum collector mounting angle, measured from horizontal, equals the latitude of the collector location. Ideal direction is true south, but in most cases, solar collectors for water heating can be mounted within 30 degrees of true south and will tolerate a small amount of shading.

Collectors are typically mounted on roofs, but also can be mounted on the ground near homes. Wind can create strong lift under collectors, so they must be securely fastened to the building or to the ground. They’re not heavy, even when filled with fluid, but make sure the roof structure is in good shape.

Sizing. Solar water heaters are rarely designed to provide 100 percent of your hot water — there are just too many cloudy days over the course of a year. Nevertheless, a typical solar water heater will provide between 50 percent and 75 percent of your annual load. In hot climates or during the sunniest times of the year, you can expect to get nearly 100 percent of your hot water from solar. During the cloudiest periods you may only get 50 percent, depending on your climate.

In cool climates, a system is sized with 20 square feet of collector and 20 gallons of storage capacity for each person in the household. For large families, this can be reduced by 10 percent for each person over four members in the household. In warm climates, a system is sized with 15 square feet of collector and 25 gallons of storage for each person in the household, with the same reductions for larger families. These sizing methods will give the best return on investment. Systems smaller than these certainly will work well, but your savings will be less.

Solar Hot Water: Warm Climates

The choice of the right type of solar water-heating system depends primarily on the climate where you live. The crucial fact is...
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